Title : Mechanical circulatory support: Modelling cannula dependent arterial inflow
Abstract:
Limb ischemia is a major complication associated with peripheral veno-arterial extracorporeal
membrane oxygenation (VA ECMO). The high velocity jet from arterial cannulae can cause
“sandblasting” injuries to the arterial endothelium, with the potential risk of distal embolization and
end organ damage.
Aim
The aim of this study was to identify, for a range of clinically relevant VA ECMO cannulae and flow
rates, any regions of peak flow velocity on the aortic wall which may predispose to vascular injury,
and any regions of low velocity flow which may predispose to thrombus formation.
Methods
A silicone model of the aortic and iliac vessels was sourced and the right external iliac artery was
cannulated. Cannulae ranged from 15 – 21 Fr in size. Simulated steady state ECMO flow rates were
instituted using a magnetically levitated pump (CentriMag pump). Adaptive particle image
velocimetry was performed for each cannula at 3, 3.5, 4 and 4.5 L/min.
Results
For all cannulae, in both horizontal and vertical side hole orientations, the peak velocity on the aortic
wall ranged from 0.3 m/s - 0.45 m/s, and the regions of lowest velocity flow were 0.05 m/s. The
magnitude of peak velocity flow on the aortic wall was not different between a single pair versus
multiple pairs of side holes. Maximum velocity flow on the aortic wall occurred earlier at a lower
pump flow rate in the vertical orientation of distal side holes compared to a horizontal position. The
presence of multiple paired side holes was associated with fewer low velocity flow regions, and
some retrograde flow, in the distal abdominal aorta compared to cannulae with a single pair of side
holes.
Conclusion
From this in vitro visualization study, the selection of a cannula design with multiple versus single
pairs of side holes did not change the magnitude of peak velocity flow delivered to the vessel wall.
Cannulae with multiple side holes were associated with fewer regions of low velocity flow in the
distal abdominal aorta. Further in vivo studies, and ideally clinical data would be required to assess
any correlation of peak velocity flows with incidence of vascular injury, and any low velocity flow
regions with incidence of thrombosis.
